An issue associated with hydrocarbon recovery is that many oil producing wellbores or the like produce and earth formations surrounding such oil wells contain mixtures of fluids. Generally, such fluid mixtures may comprise a mixture of oil and/or gas, wherein the gas is often a gaseous hydrocarbon, together with water. Said mixtures may also contain reactive chemicals and may carry mineral particles, such as sand or the like. For purposes of hydrocarbon production, it is often necessary to collect samples of or test the fluids in the wellbore or the surrounding earth formations.
In hydrocarbon production from subsurface formations, it is often necessary to collect samples of or sense physical or chemical properties of fluids either downhole in the wellbore or in the formation or formations surrounding the wellbore. For example, when a wellbore is producing hydrocarbons a production logging tool may be introduced into the wellbore to either collect samples of and/or sense the physical or chemical properties of the fluids flowing downhole in the wellbore. In other situations, a wellbore tool may be equipped with a probe to provide for downhole withdrawing of fluids from earth formations surrounding the wellbore, such as collection of fluids from hydrocarbon reservoirs and the like. In yet other examples, fluids, aggregates, mud or the like may be pumped into the wellbore and/or the surrounding earth formations to provide for changing the interaction between the wellbore and the earth formation, changing the interaction between the wellbore and the hydrocarbon reservoir and/or the like and collection of samples and/or sensing of physical and chemical properties of fluids flowing in the wellbore or surrounding earth formations after such manufactured interaction changes have been initiated may be desirable.
Downhole collection or sensing of chemical and physical properties of fluids may be problematic because of fluid mixing (fluid mixtures may make accurate sensing of physical or chemical properties of the constituent fluids in the mixture inaccurate or in some circumstances impossible—presence of contaminants in the fluids to be collected and/or sensed—wherein the contaminants may be fouling contaminants, contaminants that may adversely affect sensors or the like. Furthermore, obtaining clean samples of constituent fluids of fluid mixtures downhole for sampling and/or sensing is problematic because of the physical dimensions of wellbore tools, sampling duration in dynamic wellbore conditions, adverse physical conditions, remoteness of the sampling site and/or the like.
In the first case, a knowledge of the hydrocarbon properties as a function of the position along the wellbore is useful in deciding the production strategy for the well and is presently carried out using an MDT. In this case, the fluid is drawn from the formation and passes sensors that analyze the fluids for contamination by drilling mud and water etc. After a period of time, the contamination decreases as the pumps draw fluid from deeper in the formation. Once the contamination is below a certain level, the fluid can then be diverted into a sampling chamber for bring back to the surface for more detailed analysis. It is extremely difficult to achieve zero contamination of the formation fluid sample by near wellbore invaded fluids and the wellbore fluid itself due to the nature of the flow in the formation and around the sampling probe. Existing sensors have to be sufficiently rugged to survive all possible fluid eventualities. To make real-time measurements of the fluid (hydrocarbon) properties requires low (ideally zero) levels of contamination of the wrong phase. The ability to control the phase species and quality will allow new sensors to be used in the downhole environment, and novel membrane based sensors will be expected to survive for longer periods of time than if they had to endure the full diversity of the mixed flow as it is extracted from the formation. Methods have been proposed to allow for aggregation of the mixed flow, so that slugs of the individual phases pass the sensors (Carnegie et al. 2003) and also the use of a hydrocyclone to achieve the separation and flow split (Oddie, 2002a and 2002b). In the first, the sensors still have to endure the diverse fluids and in the second, the pressure drop and the control of the fluid split would be problematic in the downhole environment.
Current production logging methods are aimed at determining the volumetric flow rates and spatial distribution of the fluids in the wellbore, as a function of position along the oil well. These measurements may be used to diagnose production problems in all types of completions—open hole, slotted liner, screened, cased and perforated etc. However, in more complex wells, such as those where the fluids are being produced from multiple zones or very thick producing layers, a detailed knowledge of the composition of the fluids as a function of position would be very useful. Identifying different qualities of hydrocarbons, for example, would allow specific interventions to produce what is desired, rather than waiting until the co-mingled flow arrives at the surface. Similarly identifying the composition of the water as a function of position would allow determination of shortcutting etc in waterflood wells, and those producing zones that are the sources of scale forming salts. Copositional analysis using PL tools would be a new service. The device proposed here would be extremely beneficial towards the quality of the results.